Effect of the Diisocyanate Structure and the Molecular Weight of Diols on Bio-Based Polyurethanes Wannarat Panwiriyarat, 1,2 Varaporn Tanrattanakul, 1 Jean-François Pilard, 2 Pamela Pasetto, 2 Chuanpit Khaokong 1 1 Department of Materials Science and Technology, Bioplastic Research Unit, Faculty of Science, Prince of Songkla University, Songkhla 90112, Thailand 2 Institut des Mol ecules et Mat eriaux du Mans, UMR CNRS 6283, Universit e du Maine, 72085, Le Mans Cedex, France Correspondence to: V. Tanrattanakul (E-mail: varaporn.t@psu.ac.th) ABSTRACT: Bio-based polyurethanes (PU) containing poly(e-caprolactone) diol (PCL) and hydroxyl telechelic natural rubber (HTNR) were synthesized. The effect of the diisocyanate structure and the molecular weights of diols on the mechanical properties of PU were investigated. Three different molecular structures of diisocyanate were employed: an aliphatic diisocyanate (hexamethylene diisocya- nate, HDI), an aromatic diisocyanate (toluene-2,4-diisocyanate, TDI) and a cycloalkane diisocyanate (isophorone diisocyanate, IPDI). Two molecular weights of each diol were selected. When HDI was employed, a crystalline PU was generated while asymmetrical struc- tures of TDI and IPDI provided an amorphous PU. The presence of crystalline domains was responsible of a change in tensile behav- ior and physical properties. PU containing TDI and IPDI showed a rubber-like behavior: low Young’s modulus and high elongation at break. The crystalline domains in PU containing HDI acted as physical crosslinks, enhancing the Young’s modulus and reducing the elongation at break, and they are responsible of the plastic yielding. The crystallinity increased the tear strength, the hardness and the thermal stability of PU. There was no significant difference between the TDI and IPDI on the mechanical properties and the phys- ical characteristics. Higher molecular weight of PCL diol changed tensile behavior from the rubber-like materials to the plastic yield- ing. Thermal and dynamic mechanical properties were determined by using DSC, TGA and DMTA. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 453–462, 2013 KEYWORDS: biodegradable; biopolymers and renewable polymers; polyurethanes; copolymers; elastomers Received 9 August 2012; accepted 16 January 2013; published online 19 March 2013 DOI: 10.1002/app.39170 INTRODUCTION Polyurethane is generally prepared via a polyaddition reaction between a diisocyanate and a polyol to form urethane linkages. Its molecular structure and its properties vary over a broad range of stiffness or flexibility, hardness, and density, 1 conse- quently there are many applications of polyurethane such as flexible or rigid foams, chemical resistant coatings, rigid and flexible plastics, specialty adhesives and sealants, and elasto- mers, 2 all of which lead to an increase in polyurethane con- sumption. At the end of their life cycle, these synthetic polymers so widely used do not degrade naturally leading to a consider- able amount of waste and, as consequence, to environmental issues. In this context, the development of biodegradable poly- urethane is a topic of interest. Among the commercial biode- gradable polymers, such as polyhydroxyalkanoates, poly(lactic acid), and polyesteramide, poly(e-caprolactone) (PCL) diol has been widely used as a starting material for synthesizing biode- gradable polyurethane, which can now be found in many applications. 3–18 The synthesis of bio-based polyurethanes in general has gained in- terest as well. To find alternative renewable monomer feedstocks and to promote sustainable development, many bio-based polyols from renewable resources, such as plant oil, 19–23 sugar, 24 chitosan, 25 natural rubber, 26–39 chitin, 40,41 glucan, 42 and heparin 43 have been explored for polyurethane synthesis. Natural rubber can be easily chemically modified to give a functionalized rubber, such as epoxi- dized natural rubber (ENR), carbonyl telechelic natural rubber (CTNR) and hydroxyl telechelic natural rubber (HTNR). In princi- ple, a PCL-based polyurethane is a biodegradable polyurethane, whereas a HTNR-based polyurethane is a bio-based polymer and does not easily degrade; although NR is a biopolymer, its biodegra- dation has not been widely studied, we found just one article reporting the biodegradation of NR/starch blend by bacteria iso- lated from soil. 44 Therefore, if a biodegradable segment, for V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.39170 453